A carpometacarpal boss, also known as a CMC boss or “bossing,” is a lump that appears on the back of the hand. It is typically in line with the pointer or middle finger. The exact cause of it is unknown, although sometimes they can arise from a traumatic injury or repetitive wrist motion that can happen during things like golf.
Here are some signs that you have a CMC boss:
- You notice a lump on the back of your hand
- It appeared between the ages of 20 and 40
- You feel pain when moving the wrist up or down
- You feel a snapping sensation when moving the wrist